Gasoline particulate filters: what you need to know

The DPF particulate filter, which has caused so many headaches for owners of diesel cars, is now arriving on petrol engines. This is what you need to know if you are going to buy a petrol car with this system.

Already common on diesel-engined cars, where particulate filters have been in use for years, if you buy a new car with a petrol engine it is very likely to be fitted with this exhaust gas treatment system too.

But what is the difference between diesel particulate filters, or FAPs, and the new petrol particulate filters, or GPFs? Will the latter cause as many problems as the former did? What should I consider if my petrol car has a particulate filter?

We are going to review how particulate filters work and how they are applied in petrol engines, to resolve any doubts you may have… And so you have no reason to hate them, as people do with diesel engine filters.

Why do petrol cars now need filters?

The use of particulate filters in petrol engines is driven, as happened with diesels, by the introduction of increasingly strict emissions regulations.

Here, however, the change petrol engines underwent when “downsizing” became fashionable also played a big part. Manufacturers began combining direct injection and turbocharging in small-displacement engines, which were capable of delivering more performance than large-capacity naturally aspirated engines, and with greater efficiency.

Particulate filters for petrol engines are here to stay.

But, because of the way it works, burning the air and petrol mixture generates more particles. Combined with the tightening of emissions regulations, a solution had to be found. Increasing injection pressure to achieve better atomisation of the fuel, and therefore cleaner combustion, was not enough.

So, at the end of 2017, Mercedes was one of the first brands to announce the fitting of particulate filters to its petrol engines, which were incorporated in early 2018 on its S-Class. The rest of the manufacturers soon followed, initially only on engines of a certain power output and on high-end cars. But today most new engines are fitted with particulate filters, even the increasingly popular three-cylinder, small-displacement engines.

The massive adoption of this system had a deadline: in September 2018 the change from the NEDC to the WLTP homologation cycle and the Euro 6c emissions standard came into force, which set the same particulate emission limits for petrol and diesel engines.

Longer life and fewer problems than filters for diesel engines

At this point, and especially if you are going to buy a petrol-engined car because your previous diesel gave you many problems with the particulate filter, the first thing you should know is that petrol engines do not need as much attention.

In both cases the objective is to trap, retain and eliminate the solid particles generated in the combustion process, which engines emit along with other gases through the exhaust pipe. To do this, the filter has an internal honeycomb structure made of porous materials, to which the particles adhere, which the system later burns off before the filter becomes completely clogged.

The difference is that in petrol engines the temperature of the exhaust gases is higher, and it is much easier for the particles trapped by the filter to burn off passively, through continuous regeneration processes. In diesels, by contrast, forced regeneration processes are required, with small fuel injections that also increase consumption. Petrol engine filters also do not need additives such as AdBlue, which diesels do use, something that, after all, also requires special attention.

Unlike diesel engines, particulate filters in petrol-engined cars do not need AdBlue.

How to look after the GPF particulate filter of a petrol car

For all these reasons, the lifespan of particulate filters in petrol-engined cars is longer than in diesels, their maintenance is lower, and there are far fewer chances of breakdowns.

The type of fuel and the higher temperature of the exhaust gases make the operation of particulate filters in petrol engines less problematic than in diesels, as regeneration of the filter occurs more easily.

Even so, it should be borne in mind that it is a very expensive part to repair or replace in case of trouble. Therefore, to avoid faults in the GPF particulate filter of your petrol car, keep these tips in mind:

– Use quality oils. Simply make sure the oil meets or exceeds the minimum specifications recommended by the manufacturer (remember, it is better if it is a good synthetic oil). And, furthermore, it is better if they are special oils for engines with particulate filters, although they are still easier to find for diesel engines than for petrol ones. These lubricants are characterised by their low content of elements such as sulphated ash, sulphur or phosphorus. They will extend the life of your car’s particulate filter, and they do not represent a cost over conventional oil that would justify ignoring them.

– Take the car out on the open road. The most important thing is that the filter regenerates properly. To do this, just as with diesel engines fitted with a filter, do not forget that from time to time you need to take the car on the open road and let the engine run “briskly” for a few kilometres. This is not as necessary as with diesels because, as we have explained, petrol engines generate fewer particles and regeneration occurs almost continuously. But if you normally use the car in the city, it is not a bad idea to take it out on the open road at least every 300 km.